1. Field of the Invention
Generally, the present disclosure relates to the field of integrated circuits, and, in particular, to integrated circuits including resistors.
2. Description of the Related Art
Integrated circuits typically include a large number of circuit elements, which form an electric circuit. In addition to active devices such as, for example, field effect transistors and/or bipolar transistors, integrated circuits can include passive devices such as capacitors, inductivities and/or resistors.
Types of resistors that may be used in integrated circuits include resistors having a doped semiconductor region formed in a semiconductor material, wherein the doped semiconductor region is doped differently from other portions of the semiconductor material. The semiconductor material may, for example, be provided in the form of a portion of a bulk semiconductor substrate, such as a silicon wafer, or a layer of semiconductor material, for example silicon, that is provided above a layer of an electrically insulating material in a semiconductor-on-insulator (SOI) structure.
Electrical connections to the doped semiconductor region may be provided, wherein the electrical connections may be adapted to provide a substantially ohmic connection to the doped semiconductor region. Due to the doping of the doped semiconductor region that is different from the doping of other portions of the semiconductor material, a current flowing between the electrical connections may be substantially confined to the doped semiconductor region.
For a doped semiconductor region having a cross-sectional area A that is substantially constant between the electrical connections to the doped semiconductor region, the resistance of the resistor is given approximately by the equation R=ρ*A/L, wherein ρ is the specific resistivity of the doped semiconductor region and L is the distance between the electrical connections. The product ρ*A depends on the width of the doped semiconductor region, the dopant concentration in the doped semiconductor region and the depth of the doped semiconductor region.
The possibilities to reduce the width of the doped semiconductor region may be limited by a resolution of processes of photolithography. Moreover, the width of the doped semiconductor region, as well as its depth, may depend on characteristics of processes used for introducing dopants into the doped semiconductor region, such as ion implantation, and dopant diffusion processes. Since, therefore, the possibilities to reduce the width and depth of the doped semiconductor region are limited, a desired resistance R of the resistor is typically provided by adapting the dopant concentration in the doped semiconductor region and the distance L between the electrical connections to the doped semiconductor region.
The resistance R increases with increasing L, and increases when the dopant concentration is reduced. Therefore, for providing a resistor having a relatively high resistance, a compromise between low doping and relatively large dimensions of the resistor has to be found. While reducing the dopant concentration may be advantageous from the point of view of reducing the area required by the resistor, reducing the dopant concentration may lead to an increase of random dopant fluctuations. Additionally, line roughness may contribute to the variability of the resistance of a resistor device as described above.
Therefore, in the manufacturing of resistor devices as described above, providing a resistor wherein a desired value of the resistivity is obtained with a relatively high precision may be an issue.
The present disclosure provides semiconductor devices including resistors and methods for the formation thereof wherein the above-mentioned issue may be avoided or at least reduced.